The present invention relates to fuel injectors, and more particularly to an assembly and poppet for use in fuel injectors.
Conventinal fuel injectors are configured to deliver a quantity of fuel to a combustion cylinder of an engine. To increase combustion efficiency and decrease pollutants, it is desirable to atomize the delivered fuel. Generally speaking, atomization fo fuel can be achieved by supplying high pressure fuel to conventional fuel injectors, or by atomizing low pressure fuel with pressurized gas, i.e., “air assist fuel injection.”
A conventional air assist fuel injector receives a metered quantity of low pressure fuel from a conventional fuel injector (not illustrated) and pressurized air from a rail (not illustrated). The air assist fuel injector atomizes the low pressure fuel with the pressurized air as it conveys the air and fuel mixture to the combustion chamber of an engine.
The pressurized air from the rail and the metered quantity of fuel from the conventional fuel injector enter the air assist fuel injector through a cap, which delivers the fuel and air to a conduit of an armature. Thereafter, the fuel and air travel through a passageway of a fluid transportation member or poppet, and exit the poppet through small slots near the end or head of the poppet. The poppet is typically attached to the armature, which is actuated by energizing a solenoid coil. When the solenoid coil is energized, the armature will overcome the force of a spring and move. Because the poppet is attached to the armature, the head of the poppet will lift off a seat when the armature is actuated so that the metered quantity of fuel is atomized as it is delivered to the combustion chamber of the engine. Hence, besides conveying liquid fuel and air, the poppet repeatedly opens to inject fuel and closes to define a seal that prevents the injection of fuel. Because of this function, the poppet is a critical component of most fuel injectors and is typically fabricated from a high strength, tough, and wear resistant material, such as AISI 440 stainless steel. For example, the conventional poppet is typically formed from stainless steel bar stock by: (1) machining the bar stock to a cylindrical blank; (2) gun-drilling the internal cylindrical passageway of the poppet; (3) heat treating the part; (4) grinding the exterior surface of the poppet; and (5) electrical discharge machining (“EDM”) the slots. Unfortunately, it was discovered that the intersection between the gun-drilling of the internal passageway and the formation of the slots in the poppet via the EDM process produces stress concentration areas. These stress concentration areas, in conjunction with the micro-cracks typically resulting from the EDM process, have caused the poppet to fail at or near the slots. Additionally, it is difficult to bore the internal and elongated passageway of the poppet and there are reported failures due to excessive run-out during this operation. Despite these problems, the above-described manufacturing process was thought to be the only suitable method of manufacturing the poppet, largely because the shape, features, and requirements of conventional poppets are not well-suited for other, traditional fabrication processes.